1. Field of the Invention
The invention relates to farm machines such as mowers or harvesters. In particular, the present invention provides an improved load-lightening and lifting device which includes a jack or lift cylinder arrangement mounted parallel with an elastically deformable element. The jack includes a cylinder; a rod guided in the cylinder and coming out or extending from the cylinder; and a piston mounted to slide in the cylinder and which separates the cylinder into two distinct chambers, at least one of which is intended to be fed with fluid from a feed source to translate the piston in the cylinder.
2. Discussion of Background
DE-31 39 936 shows a farm machine which rests on the ground by two wheels. The two wheels are connected to the frame of the machine by two wheel arms fastened to a pivoting shaft. The pivoting shaft is connected to the frame to allow a simultaneous pivoting of the wheel arms around the geometric axis of the pivoting shaft.
This known machine also includes a jack or lift cylinder arrangement and a helical compression spring. The jack is installed between the frame and a first lever connected rigidly to the pivoting shaft, to pivot the wheel arms downward, and move the frame away from the ground. So that the jack does not prevent, during work, a displacement in height of the frame in relation to the wheels, an operational play between the rod of the jack and the first lever is provided. This operational play allows a slight pivoting of the first lever, and therefore of the wheel arms in relation to the frame. In addition, a second lever is connected to the first lever by a hinge directed parallel to the pivoting shaft of the wheel arms. Furthermore, the helical spring extends between this second lever and the frame. Under the action of this helical spring, the second lever rests on one of the wheel arms to lighten the frame during work.
Since this known machine comprises a spring mounted parallel with a jack, the space requirement with respect to the length of the spring-jack unit is relatively small. Moreover, in a first mode of operation, the helical spring lightens the frame, whereas the action of the jack is cancelled, while in a second mode of operation, the frame is brought into a raised position by the jack.
However, this known machine exhibits certain drawbacks.
With regard to the operational play that is provided between the jack and the first lever, the connection between the jack and the first lever is relatively complex. Furthermore, taking into account the environment in which work is generally performed with this type of farm machine, the operational play of this connection runs the risk of being quickly obstructed or hindered by deposits and debris, which would interfere with good load-lightening of the machine. In addition, the use of a second lever upon which the spring acts is also relatively complex.